Image processing device, method, program

Abstract

The present invention provides an image processing device that achieves appropriate color reproduction in printed materials that have been printed using image data. [Solution] The image processing apparatus includes a first color conversion means that, when the image represented by the input image data includes a gradient region having a gradient between a first color value and a second color value, and the region of the image other than the gradient region includes a first solid region having only the first color value and a second solid region having only the second color value, performs color conversion on the first solid region and the second solid region using a first color conversion method, and performs color conversion on the gradient region using a second color conversion method. As a result of the color conversion performed by the first color conversion means, the color difference between the first solid region and the second solid region is greater than the color difference between the region corresponding to the first color value and the region corresponding to the second color value in the gradient region.

Description

Technical Field

[0006] , ,

[0005] , ,

[0001] The present invention relates to an image processing apparatus, method, and program capable of performing gamma mapping.

Background Art

[0002] There is known a printer that receives a digital manuscript described in a predetermined color space, performs mapping of each color in the color space to a color reproduction range reproducible by the printer, and outputs the result. For example, there is known a method of identifying an object in a manuscript, performing "colorimetric" mapping on a graphic area, and performing "perceptual" mapping on a photographic area. However, it is very difficult to identify an object, and especially when a plurality of objects overlap, one of the above mappings is selected for the object with merged areas.

[0003] Patent Document 1 describes analyzing manuscript data to be recorded and dividing the manuscript data into a plurality of partial manuscript data. Then, based on the pixel values included in the partial manuscript and the color reproduction range (color gamut) at the time of recording for each partial manuscript data, a color mapping method (color conversion method) for the partial manuscript to a color reproduction range reproducible by the printer is set and color conversion is performed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When image data including a gradation area and a solid area is input, it is required to enhance the discriminative color reproduction of the solid area while reproducing the gradation property of the gradation area.

[0006] The present invention aims to provide an image processing apparatus, method, and program that achieve appropriate color reproduction in printed materials printed with image data. [Means for solving the problem]

[0007] The image processing apparatus according to the present invention is an image processing apparatus comprising: an input means for inputting image data; and a first color conversion means that, when the image data input by the input means includes a gradient region having a gradient between a first color value and a second color value, and the region of the image other than the gradient region includes a first solid region having only the first color value and a second solid region having only the second color value, performs a color conversion on the first solid region and the second solid region using a first color conversion method, and performs a color conversion on the gradient region using a second color conversion method, wherein the color conversion by the first color conversion means is a conversion from the color gamut represented by the image data to a color gamut reproducible by the image processing apparatus, and as a result of the color conversion by the first color conversion means, the color difference between the first solid region and the second solid region is greater than the color difference between the region corresponding to the first color value and the region corresponding to the second color value in the gradient region. [Effects of the Invention]

[0008] According to the present invention, appropriate color reproduction can be achieved in printed materials on which image data has been printed. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram showing the configuration of an image processing device. [Figure 2] This is a diagram illustrating the recording head. [Figure 3] This is a flowchart showing the processing in an image processing device. [Figure 4] This is a diagram to explain partial manuscript data. [Figure 5] This is a flowchart showing the processing in an image processing device. [Figure 6] A diagram showing the input image data. [Figure 7] A diagram for explaining color degradation and its correction. [Figure 8] A diagram for explaining the setting process of the second region. [Figure 9] A diagram showing the second region. [Figure 10] A flowchart showing the processing in the image processing apparatus. [Figure 11] A diagram showing the printing result. [Figure 12] A flowchart showing the processing in the image processing apparatus. [Figure 13] A diagram showing the input image data. [Figure 14] A diagram for explaining color degradation and its correction. [Figure 15] A diagram showing the third region. [Figure 16] A diagram showing the first region, the second region, and the third region. [Figure 17] A diagram showing the printing result. <000008​​​​​​​​​​​​​​​​​​​​​Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and duplicate explanations are omitted.

[0011] [First Embodiment] Regarding the terms used in this embodiment, they are defined as follows in advance.

[0012] (Color Reproduction Region) The color reproduction region refers to the range of reproducible colors in an arbitrary color space. It is also referred to as the color reproduction range, color gamut, or gamut. Further, as an index representing the size of this color reproduction region, there is a gamut volume. The gamut volume is the three-dimensional volume in an arbitrary color space. The chromaticity points constituting the color reproduction region may be discrete. For example, a specific color reproduction region may be represented by 729 points on CIE-L*a*b*, and for the points in between, known interpolation operations such as tetrahedron interpolation or cube interpolation may be used to obtain them. In such a case, the corresponding gamut volume can be the volume obtained by calculating and accumulating the volumes on CIE-L*a*b* such as tetrahedrons or cubes corresponding to the interpolation operation method that constitute the color reproduction region. The color reproduction region and color gamut in this embodiment are not limited to a specific color space, but in this embodiment, the color reproduction region in the CIE-L*a*b* space is described as an example. Similarly, the numerical values of the color reproduction region in this embodiment indicate the volume calculated cumulatively in the CIE-L*a*b* space on the premise of tetrahedron interpolation.

[0013] (Gamut Mapping) Gamut mapping is the process of converting between different color gamuts. For example, it involves mapping an input color gamut to an output color gamut. Conversion within the same color gamut is not called gamut mapping. Common ICC (International Color Consortiaum) profiles include Perceptual, Saturation, and Colorimetric. The mapping process can be performed using a single 3D 3DLUT (Look Up Table). Alternatively, the color space can be converted to a standard color space before the mapping process. For example, if the input color space is sRGB, it can be converted to the CIE-L*a*b* color space. The mapping process is then performed on the output color gamut within the CIE-L*a*b* color space. The mapping process can be done using a 3DLUT or a conversion formula. It is also possible to convert between the input and output color spaces simultaneously. For example, the input color space may be sRGB, and the output may be converted to RGB or CMYK values ​​specific to the recording device.

[0014] (Color degeneration) In this embodiment, when gamut mapping is performed on any two colors, color degeneracy is defined as the case where the distance between the mapped colors in a predetermined color space becomes smaller than the distance between the colors before mapping. Specifically, suppose there are colors A and B in a digital original, and by mapping to the printer's color gamut, color A is converted to color C and color B is converted to color D. In this case, color degeneracy is defined as the case where the distance between color C and color D becomes smaller than the distance between color A and color B. When color degeneracy occurs, colors that were recognized as different in the digital original may be recognized as the same color when the image is recorded. For example, in a graph, different items are recognized as different items by using different colors. When color degeneracy occurs, different colors are recognized as the same color, which can lead to the misconception that different items in a graph are the same item (a decrease in discriminability). The predetermined color space used to calculate the distance between colors here can be any color space. Examples include the sRGB color space, Adobe RGB color space, CIE-L*a*b* color space, CIE-LUV color space, XYZ color system color space, xyY color system color space, HSV color space, and HLS color space.

[0015] <Overall image processing device> Figure 1 shows the overall configuration of a print system to which the image processing apparatus of this embodiment is applied. It includes a personal computer device (PC) 101 (hereinafter also referred to as "PC") and a printing device 108. The PC 101 performs print control instructions to the printing device 108, transfers necessary information and data, etc. The storage device 105 stores and manages the OS, system programs, various application software, and parameter data necessary for various processes. A hard disk or flash ROM can be used as this storage device 105. The CPU 102 uses the working memory 104 to execute the software stored in the storage device 105. The user interface (hereinafter also referred to as "UI") 103 performs processing related to user input and display to the user in relation to the execution of the above processes, and includes input devices such as a keyboard and mouse, and display devices such as a display. The data input / output device 106 performs data input and output to an external storage medium such as an SD card. Alternatively, an imaging device (not shown) may be directly connected to the data transfer I / F 106 or data transfer I / F 110 to transfer data without using an external storage medium.

[0016] The PC 101 and the printing device 108 are connected via a communication line 107. In this embodiment, a local area network is described as an example of the communication line 107, but it may also be a USB hub, a wireless communication network using a wireless access point, or a connection using Wi-Fi® direct communication function.

[0017] The original document data to be printed, which is transferred to the printing device 108, is in a data format standardized by, for example, PDF (Portable Document Format) or PWG-Raster. PWG-Raster is a data format standardized by PWG (Printer Working Group). In this embodiment, the PWG-Raster data format is used. The original document data, or the image data contained in the original document data, is stored as bitmap data according to the data format and does not include pixel-level type information (information indicating the attributes of pixels (e.g., information such as characters, photographs, lines)). In this embodiment, an example of the PWG-Raster data format is shown, but it is not limited to this. Any image data that does not include type information is acceptable; for example, the image data may be described in JPEG (Joint Photographic Experts Group) data, which does not include pixel-level type information, in the PDF data format. Also, the image data only needs to be image data that does not include type information in at least part. As shown in Figure 4(a) described later, when the image data is described in PDL (Page Description Language), which is a page description language, area 201 or area 202, which are area units determined by drawing commands, may have attributes such as characters or images added during rendering. However, there are cases where the area is not divided into areas 201 and 202, and the entire page 200 is configured as a single JPEG image in the PDF file. In this case, individual attributes such as area 201 being lines and area 202 being a photograph are not assigned. Therefore, as described above, if the entire page, or for example, only area 201, is an area of ​​image data that does not contain type information such as JPEG, this embodiment can be applied to that area. In this embodiment, an example is shown where the entire image data does not contain type information, but if at least a part of the image data does not contain type information, it may be applied only to that area.

[0018] The printing device 108 interprets the original data sent from the PC 101 and performs image processing on the generated image data. In the printing device 108, the CPU 111 comprehensively controls the printing device 108 by reading programs stored in the storage medium 113 into the RAM 112, which serves as a work area, and executing them. The image processing accelerator 109 is hardware capable of performing image processing at a faster speed than the CPU 111. The image processing accelerator 109 is activated when the CPU 111 writes the parameters and data necessary for image processing to a predetermined address in the RAM 112. After reading the above parameters and data, the image processing accelerator 109 performs image processing on that data. However, the image processing accelerator 109 is not an essential element, and equivalent processing may be performed by the CPU 111. The above parameters may be stored in the storage medium 113, or in storage such as flash memory or an HDD (not shown).

[0019] Here, we will describe the image processing performed by the CPU 111 or the image processing accelerator 109. Image processing is the process of generating data indicating the ink dot formation position for each scan by the recording head 115, based on the acquired document data. The CPU 111 or the image processing accelerator 109 performs, for example, color separation and quantization processing of the image data.

[0020] The color separation process is a process that separates the image into ink densities that can be handled by the printing device 108. For example, if the image data represents the image using color space coordinates such as sRGB, which is the color representation of a monitor, the data representing the image using those sRGB color coordinates (R, G, B) is converted into ink data that can be handled by the printing device 108 through the color separation process. The color conversion method is realized by matrix calculation processing, processing using a three-dimensional lookup table (3DLUT), or processing using a four-dimensional 4DLUT.

[0021] The printing apparatus 108 of this embodiment uses black (K), cyan (C), magenta (M), and yellow (Y) inks as an example. Therefore, the RGB signal image data is converted into ink data (recording data) consisting of 8-bit color signals for each of K, C, M, and Y. Each color signal corresponds to the amount of each ink applied. Although four colors, K, C, M, and Y, are given as an example of the number of ink colors, other ink colors such as light cyan (Lc), light magenta (Lm), and gray (Gy) inks with lower densities may be used to improve image quality. In that case, ink data corresponding to those colors will be generated.

[0022] After the color conversion process, the ink data is subjected to quantization. Quantization is a process that reduces the number of gradation levels in the ink data. In this embodiment, quantization is performed using a dither matrix, which is an array of thresholds for comparing with the ink data values ​​for each pixel. After the quantization process, binary data is ultimately generated that indicates whether or not a dot is formed at each dot formation position.

[0023] After image processing, the recording head controller 114 transfers binary data to the recording head 115. Simultaneously, the CPU 111 controls the recording process via the recording head controller 114, operating the carriage motor that moves the recording head 115 and the transport motor that transports the recording medium. The recording head 115 scans the recording medium, and simultaneously, ink droplets are ejected onto the recording medium by the recording head 115, thereby recording an image.

[0024] Hereinafter, the recording head 115 will be described as having recording nozzle rows for four color inks: cyan (C), magenta (M), yellow (Y), and black (K).

[0025] Figure 2 is a diagram illustrating the recording head 115 in this embodiment. In this embodiment, an image is recorded in multiple scans of N times for a unit area of ​​one nozzle row. The recording head 115 has a carriage 116, nozzle rows 117, 118, 119, and 120, and an optical sensor 122. The carriage 116, which is equipped with five nozzle rows 117, 118, 119, and 120 and the optical sensor 122, is capable of reciprocating along the main scanning direction (X direction in the figure) by the driving force of a carriage motor transmitted via a belt 121. As the carriage 116 moves in the X direction relative to the recording medium, ink droplets are ejected from each nozzle of the nozzle row in the direction of gravity (Z direction in the figure) based on the recorded data. In this embodiment, the ejection element that ejects ink droplets from each nozzle is a thermal type that generates bubbles using an electrothermal conversion element to eject liquid. However, it is not limited to this, and an ejection element that ejects liquid using a piezoelectric element (piezo) or other ejection methods may also be used.

[0026] As a result, an image equivalent to 1 / N (N: a natural number) main scans is recorded on the recording medium placed on the platen 123. Once one main scan is completed, the recording medium is transported in the transport direction (Y direction in the figure) intersecting the main scan direction by a distance corresponding to the width of 1 / N main scans. Through these operations, an image is recorded in N scans over an area the width of one nozzle row. By repeating these main scan and transport operations alternately, an image is gradually recorded on the recording medium. In this way, it is possible to control the process to complete the image recording for a predetermined area.

[0027] <Recording process> Figure 3 is a flowchart illustrating the recording process in the printing device 108. The process shown in Figure 3 is achieved, for example, by the CPU 111 executing a program read from the RAM 112.

[0028] In S101, the CPU 111 acquires the document data to be recorded. Specifically, for example, the CPU 111 acquires the document data from the PC's data transfer interface 106 via the printer's data transfer interface 110. Here, the document data is a document consisting of multiple pages.

[0029] Next, in S102, the CPU 111 divides the original data into multiple partial original data. In this embodiment, the original data to be recorded is, for example, document data consisting of multiple pages. The partial original data can take any form as long as it is a processing unit into which the original data has been divided. Figure 4 is a diagram illustrating partial original data. For example, a page unit may be used as partial original data, as shown in page 200 in Figure 4(a). Figure 4(b) shows the recording area recorded by scanning with the recording head 115. Area 204 shows an example where recording is completed in two scans by the recording head 115 (arrows indicate scanning direction). Data in units recorded by the recording head, such as area 204, may also be used as partial original data. Furthermore, if the image data in Figure 4(a) is described in PDL, a page description language, area 201 or area 202, which are area units determined by drawing commands, may be used as partial original data. Also, for example, if it is a page unit, multiple area units determined by pages, bands, and drawing commands may be combined into one partial original data, such as combining the first and second pages to form partial original data. This embodiment shows an example of dividing the manuscript data into partial manuscript data on a page-by-page basis.

[0030] Next, in S103, CPU111 performs a loop process that is executed for each portion of the original document data. In S103, CPU111 performs a color conversion process on the portion of the original document data. Details of the color conversion process will be described later.

[0031] Next, in S104, the CPU 111 determines whether the color conversion of all partial document data has been completed. If it is determined that it has been completed, the process moves to S105; if it is determined that it has not been completed, the color conversion process in S103 is performed on the next partial document data. Next, in S105, the CPU 111 records the document data. Specifically, for example, for each pixel of the image data converted in S103, it performs four processes: ink color separation, output characteristic conversion, quantization, and recording.

[0032] Ink color separation is a process that converts the output values ​​Rout, Gout, and Bout from the color conversion process into the output values ​​of each ink color to be recorded by the inkjet recording method. In this embodiment, for example, recording with four inks, cyan, magenta, yellow, and black, is assumed. There are various ways to implement this conversion. For example, similar to the color conversion process, a 3D LUT is used to calculate a suitable combination of ink color pixel values ​​(C, M, Y, K) for a given combination of output pixel values ​​(Rout, Gout, Bout). For example, the following 3D LUT2

[0256]

[0256]

[0256] [4] is used.

[0033] C=LUT2[Rout][Gout][Bout][0]...(1) M=LUT2[Rout][Gout][Bout][1]...(2) Y=LUT2[Rout][Gout][Bout][2]...(3) K=LUT2[Rout][Gout][Bout][3]...(4) Alternatively, the number of LUT grids can be reduced from 256 grids to, for example, 16 grids, and the output value can be determined by interpolating the table values ​​of multiple grids, thereby reducing the table size.

[0034] Next, the output characteristic conversion is a process that converts the density of each ink color into the rate of recording dots. Specifically, for example, the density of each color with 256 gradations is converted into the rate of recording dots Cout, Mout, Yout, and Kout, which have 1024 gradations for each color. For this purpose, a one-dimensional LUT3[4]

[0256] is used, for example, which sets a suitable rate of recording dots for each ink color density, as shown below.

[0035] Cout=LUT3[0][C]···(5) Mout=LUT3[1][M]···(6) Yout=LUT3[2][Y]···(7) Kout=LUT3[3][K]···(8) Alternatively, the number of LUT grids can be reduced from 256 grids to, for example, 16 grids, and the output value can be determined by interpolating the table values ​​of multiple grids, thereby reducing the table size.

[0036] Next, quantization is the process of converting the recording dot ratios Cout, Mout, Yout, and Kout for each ink color into the On / Off state of the actual recording dots of each pixel. Various methods can be used for quantization, such as the error diffusion method and the dithering method. For example, the dithering method can be used to achieve this as shown in the following equation.

[0037] Cdot=Halftone[Cout][x][y]···(9) Mdot=Halftone[Mout][x][y]···(10) Ydot=Halftone[Yout][x][y]···(11) Kdot=Halftone[Kout][x][y]···(12) Then, by comparing the data with a threshold corresponding to each pixel position (x,y), the On / Off state of each ink color recording dot is achieved. Here, for example, Cout, Mout, Yout, and Kout are each represented by 10 bits and take values ​​in the range of 0 to 1023. Therefore, the occurrence probability of each recording dot is Cout / 1023, Mout / 1023, Yout / 1023, and Kout / 1023. Finally, recording is performed based on the generated binary data.

[0038] <Color conversion process> Figure 5 is a flowchart illustrating the color conversion process S103 in Figure 3 in the first embodiment. The process in Figure 5 is realized, for example, by the CPU 111 executing a program read from RAM 112.

[0039] In S201, CPU 111 acquires image data for color conversion processing. The image data acquired in this embodiment is partial original data output from S102, for example, page-level image data. The image data contains color information representing colors defined in a predetermined color space. In this embodiment, the image data is sRGB data containing color information defined in the sRGB space. The image data is not limited to this, however, and can be any format as long as a color space can be defined, such as Adobe RGB data, CIE-L*a*b* data, CIE-LUV data, XYZ color system data, xyY color system data, HSV data, HLS data, etc.

[0040] Next, in S202, the CPU 111 performs color conversion on the image data using a color conversion table previously stored in the storage medium 113. In this embodiment, color conversion involves gamut mapping to the image data, which maps the color reproduction range of sRGB data to the color reproduction range of the printing device 108. The printing device 108 has different color reproduction ranges depending on the recording method and recording speed determined for each output mode. Therefore, the printing device 108 requires gamut mapping that supports multiple output modes. The image data after gamut mapping is stored in the RAM 112 or the storage medium 113. Specifically, for example, the color conversion table (gamut mapping table) is a 3D LUT. The 3D LUT can calculate combinations of output pixel values ​​(Rout, Gout, Bout) for combinations of input pixel values ​​(Rin, Gin, Bin). When the input values ​​Rin, Gin, and Bin each have 256 gradations, it is preferable to use the color conversion table LUT1

[0256]

[0256]

[0256] [3] which has a total of 16,777,216 output values ​​(256 × 256 × 256). Specifically, color conversion using a gamut mapping table can be achieved in S101 by executing the following formula for each pixel of the image composed of the RGB pixel values ​​of the input image data.

[0041] Rout = LUT1[Rin][Gin][Bin][0]...(13) Gout = LUT1[Rin][Gin][Bin][1]...(14) Bout = LUT1[Rin][Gin][Bin][2]...(15) Alternatively, the number of LUT grids can be reduced from 256 grids to, for example, 16 grids, and the table size can be reduced by interpolating the table values ​​of multiple grids to determine the output value.

[0042] In S203, the CPU 111 sets two regions from the image data acquired in S201: a first region to which the color conversion method set in the subsequent S203 is applied, and a second region to which the color conversion method set in S203 is not applied. Here, the region to which a color conversion table that prioritizes color discrimination is not applied is defined as the second region. The second region is, for example, a region that prioritizes color gradation.

[0043] Figure 6 shows an example of image data 601 acquired in S201 in this embodiment. Image data 601 includes a gradient region 602, a first solid region 603, and a second solid region 604, with the remaining areas being white. The color of the first solid region 603 is also called color 603. The color of the second solid region is also called color 604. The gradient region 602 is an area where a horizontal gradient is drawn. The color of the leftmost 605 of the gradient region 602 is color 603, which is equal to the color value of the first solid region, and the color of the rightmost 606 is color 604, which is equal to the color value of the second solid region. Between the leftmost 605 and the rightmost 606, there are pixels with a gradient where the brightness changes continuously between color 603 and color 604.

[0044] In this embodiment, the solid area is defined as an area of ​​image data with the same color value, comprising at least two pixels vertically and at least two pixels horizontally. This is because, if the resolution recorded by the printing device is low, or if the amount of ink droplets formed on the recording medium (however, not limited to ink droplets as long as an image can be formed on the recording medium) is large, then even with only two pixels vertically and two pixels horizontally, a solid area can be recognized by a human on the recording medium. Therefore, depending on the resolution recorded by the printing device 108 and the amount of ink droplets, the number of pixels in the image data of the solid area may be at least two pixels vertically and at least two pixels horizontally. In addition, in this embodiment, the gradient area 602, the first solid area 603, and the second solid area 604 are surrounded by white data. White data refers to data with values ​​such as R=255, G=255, and B=255 in the case of 8-bit RGB data. The white data only needs to be surrounded by at least two pixels, similar to the solid area, so that a human can recognize it as a gradient area or a solid area.

[0045] Figure 7 is a diagram illustrating color degradation and its improvement (elimination). Figure 7 shows the case where the image data before color conversion is as shown in Figure 6. The color reproduction range 701 is the color reproduction range of the image data, and in this embodiment, it shows the sRGB color reproduction range. The color reproduction range 702 is the color reproduction range after the color conversion process in S205, which will be described later, and corresponds to the color reproduction range (device color gamut) in a predetermined output mode of the printing device 108.

[0046] In Figure 7, color 703 is the color obtained by color conversion of color 603 using gamut mapping. Color 704 is the color obtained by color conversion of color 604 using gamut mapping. In this embodiment, color degeneration is determined when the color difference ΔE705 between color 703 and color 704 is smaller than the color difference ΔE706 between color 603 and color 604. In this embodiment, color degeneration is determined when the color difference obtained by gamut mapping to the color reproduction range in a predetermined output mode of the printing device 108 is smaller than the color difference in the color reproduction range of the image data. However, this is not the only way to determine color degeneration. For example, a coefficient may be applied to either of the color differences in the two color reproduction ranges before determining color degeneration. This makes it possible to adjust the amount of color degeneration correction when the difference in color differences between the two color reproduction ranges is too large. Also, in this embodiment, an example is shown where both color 603 and color 604 are outside the color reproduction range 702 (outside the color gamut) in a predetermined output mode of the printing device 108. This is not the only way to do this; both color 603 and color 604 may be within the color gamut 702, or one of color 603 or color 604 may be outside the color gamut 702. Color degradation is more likely to occur when at least one of color 603 or color 604 is outside the color gamut 702. This is because colors outside the color gamut require gamut mapping in order to reproduce the color within the color gamut 702.

[0047] The method for calculating the color difference ΔE uses the Euclidean distance in the color space. In this embodiment, as an example, we will explain using the Euclidean distance (hereinafter referred to as color difference ΔE) in the CIE-L*a*b* color space. Since the CIE-L*a*b* color space is a visually uniform color space, the Euclidean distance can be approximated as the amount of color change. Therefore, humans perceive colors as getting closer when the Euclidean distance in the CIE-L*a*b* color space is small, and as colors as they are getting farther apart when the Euclidean distance is large. Color information in the CIE-L*a*b* color space is represented by a three-axis color space of L*, a*, and b*, respectively. The formula for calculating the color difference ΔE between color (L1, a1, b1) and color (L2, a2, b2) is the formula below. TIFF2026114577000002.tif12106...(16) When a color conversion table prioritizing color gradation, pre-stored in the storage medium 113 in S202, is applied to the gradient region 602 in Figure 6, a smooth gradient connecting color 703 to color 704 in Figure 7 is output from the printing device 108. Even if color degradation occurs because color 603 and color 604 in the gradient region 602 are printed as color 703 and color 704, if a smooth gradient connecting color 703 and color 704 is printed, the printed result will not appear unnatural. On the other hand, if color 603 in the first solid area 603 is output as color 703 and color 604 in the second solid area is output as color 704, the discriminability of the first solid area 603 and the second solid area 604 when printed will decrease compared to the digital original due to color degradation.

[0048] Therefore, in this embodiment, a color conversion table is generated that corrects color degeneracy by increasing the intercolor distance between color 703 and color 704 in a predetermined color space. Specifically, a correction process is performed to increase the intercolor distance between color 703 and color 704 beyond the intercolor distance at which they can be distinguished as different colors based on human visual characteristics. Based on human visual characteristics, the intercolor distance at which they can be distinguished as different colors is a color difference ΔE of 2.0 or more according to CIE76 (a standard for color spaces adopted by the International Commission on Illumination). Therefore, it is desirable that the color difference between color 703 and color 704 is approximately the same as a color difference ΔE of 706. For this reason, a color conversion table is generated in which color 603 is gamut-mapped to color 707 and color 604 is gamut-mapped to color 708. As a result, a color difference ΔE of 709, which is equal to a color difference ΔE of 706, can be reproduced in the device color gamut.

[0049] Next, the setting of the second region in S203, which does not apply a color conversion table that prioritizes color discrimination, will be explained using Figure 8. As shown by the arrows in Figure 8(a), line processing is performed sequentially on pixel-level image data. In the pixel-level processing, as shown in Figure 8(b), it is determined whether the color information of the three surrounding pixels (pixels 801, 802, and 803) of the pixel of interest (the pixel to be processed) 800 is continuous with the color information of the pixel of interest. In this embodiment, if the color information of each of the three surrounding pixels of the pixel of interest 800 is not identical to the color information of the pixel of interest 800, and the color difference ΔE is not 2.0 or more, the pixel of interest is set as the second region. Pixels that have already been set as the second region may be reset as the second region in the pixel-level processing. In this embodiment, the second region is set using the sequential processing described above. However, the process is not limited to the above as long as a region in which the color information changes continuously as image data can be set. For the image data in Figure 6, the gradient region 602 is set as the second region. Figure 9 shows the second region set by the processing in S203. In other words, the area filled in black in Figure 9 (i.e., the gradient area 602) is set as the second area, and the area filled in white (i.e., the area other than the gradient area) is set as the first area. S202 and S203 may be executed in parallel.

[0050] Next, in S204, the CPU 111 generates color conversion tables for the first and second regions set in S203. The color conversion table for the first region set in S203 is generated based on the following information.

[0051] Image data acquired by S201 • Color conversion table used in S202, which is pre-stored in the storage medium 113. • Image data color-converted using a color conversion table pre-stored in the storage medium 113 in S202. • Area information set in S203 For the second region, a color conversion table that prioritizes gradation, which is pre-stored in the storage medium 113 and is different from the color conversion table pre-stored in the storage medium 113 used in S202, is set.

[0052] Here, examples of the color conversion table pre-stored in the storage medium 113 used in S202 and the gradation-prioritizing color conversion table pre-stored in the storage medium 113 will be explained using Figures 20(a) to 20(d).

[0053] Figure 20(a) shows the relationship between the color space of the standard display and the color space of the recording device 108. This is generally called color space compression (color mapping). There are several methods of color space compression, and they are used depending on the purpose. In Figure 20(a), WP2003 and WP2004 are the brightest colors (white points) within the color reproduction range of the standard display and the recording device 108, respectively. Also, BP2005 and BP2006 are the darkest colors (black points) within the color reproduction range of the standard display and the recording device 108, respectively.

[0054] Figure 20(b) illustrates an example of a color conversion method applied to areas where color gradation is important. As shown by the solid line 2007 in Figure 20(b), the white point and black point of the standard display are mapped to the white point and black point of the color reproduction gamut of the recording device 108, respectively. Other colors are then converted in a way that maintains their correlation with the white point and black point. The color conversion is performed by compressing the saturation in the color direction so that the entire color space 2001 of the standard display fits within the color reproduction gamut 2002 of the recording device 108. Therefore, colors in the color space 2001 of the standard display are converted to the thick line 2007, and colors in the original color reproduction gamut 2002 are converted to the dashed line 2008. The color conversion method in Figure 20(b) is suitable for processing image data such as photographs with a large number of colors. In Figure 20(b), color compression is applied to almost the entire color gamut of the standard display in terms of both brightness and saturation.

[0055] Figure 20(c) is a diagram illustrating an example of a color conversion method applied to areas where color discrimination is important, as used in S202. As shown in Figure 20(c), this method does not perform color compression on colors within the color reproduction gamut of the recording device 108, but performs color compression on colors outside the color reproduction gamut using both brightness and saturation. The thick arrows in Figure 20(c) represent the color compression process. Multiple colors contained within the thick arrows were represented as different colors on the standard display, but after mapping, they may become the color at the end of the arrow, resulting in color degradation. For areas where color discrimination is important, the color conversion method shown in Figure 20(d) may also be applied. As shown in Figure 20(d), this method maps only the white point of the standard display to the white point of the recording device 108, and then performs color compression on colors outside the print color gamut using both brightness and saturation, without performing color compression on colors within the color reproduction gamut of the recording device 108. This method aims to reproduce the relative color difference between each color and white on a standard display as the relative color difference between each color and white paper during printing, and is called "relative colorimetric." In this color conversion method as well, multiple colors contained within the thick arrow may appear as different colors on a standard display, but after color conversion, they may become the same color at the end of the arrow, resulting in color degradation.

[0056] Next, in S205, CPU111 performs color conversion based on the following information.

[0057] • Area information set in S203 • Color conversion table for the first region set in S204 • A color conversion table that prioritizes color gradation, pre-stored in the storage medium 113, for the second area set in S204. In this embodiment, for the first region set in S203, the image data acquired in S201 is converted to color image data by performing calculations using the color conversion table for the first region set in S204. On the other hand, for the second region set in S203, the image data converted to color is generated by performing calculations using the color conversion table that prioritizes color gradation and is pre-stored in the storage medium 113, set in S204. The generated image data is stored in the RAM 112 or the storage medium 113.

[0058] <Setting the color conversion method (generating a color conversion table)> A method for generating a color conversion table that reduces the color degradation set in the first region of S204 will be explained in detail using the flowchart in Figure 10. The process in Figure 10 is realized, for example, by the CPU 111 executing a program read from RAM 112.

[0059] In S301, the CPU 111 detects the color information of the first region in Figure 9, which was set in S203. The detection process is repeated for each pixel of the image data in the first region, and is performed for all pixels included in the image data of the first region. In this embodiment, colors 603 and 604 in Figure 6 are detected. The list of color information is initialized at the start of S301.

[0060] In S302, the CPU 111 detects the number of color combinations that exhibit color degeneration based on the color information list detected in S301. Here, as explained in Figure 7, the combination of color 603 and color 604 is detected as degenerate.

[0061] In S303, the CPU 102 determines whether the number of color combinations that are color-degraded in S302 is zero. If it is determined that the number of color combinations that are color-degraded is zero, the process proceeds to S304, and it is determined that the image data does not require color degradation correction. In that case, the color conversion table is set to the color conversion table that was used in S202 and is stored in the storage medium 113 in advance. If it is determined that the number of color combinations that are color-degraded is not zero, the process proceeds to S305, and the CPU 111 performs color degradation correction.

[0062] Color degeneracy correction will cause color changes. As a result, color changes will occur even for color combinations that are not color degenerated, resulting in unwanted color changes. Therefore, the necessity of color degeneracy correction can be determined from the total number of color information list combinations and the number of color degeneracy combinations. Specifically, for example, if the number of color degeneracy combinations is more than half of the total number of combinations in the color information list, it may be determined that color degeneracy correction is necessary (i.e., color degeneracy correction is determined in S303). By doing so, the harmful effects of color changes due to color degeneracy correction can be suppressed. For example, in Figure 6, solid areas are shown for two colors, 603 and 604. If 10 solid areas are shown, the total number of combinations is 45. In that case, if the number of color degeneracy combinations is, for example, 23 or more, it may be determined that color degeneracy correction is necessary.

[0063] In S305, the CPU 111 performs color degeneration correction on color combinations that undergo color degeneration based on the image data, the image data after color conversion, and the color conversion table. As explained in Figure 7, the color difference ΔE705 between color 703 and color 704 is corrected to ΔE709 between color 707 and color 708, which is approximately the same as the color difference ΔE706. The color degeneration correction process is repeated for each color combination that undergoes color degeneration. The results of the color degeneration correction for each color combination are stored in a table that associates the pre-correction color information with the post-correction color information. In Figure 7, the color information is in the CIE-L*a*b* color space. Therefore, the color space of the input image data and the output image data may be converted. In that case, the pre-correction color information in the input image data's color space and the post-correction color information in the output image data's color space are stored in a table that associates them.

[0064] Furthermore, although Figure 7 shows the extension line between color 703 and color 704, this embodiment is not limited to this. The color difference ΔE709 between color 707 and color 708 can be in any direction in the CIE-L*a*b* color space, such as the lightness direction, chroma direction, or hue angle direction, as long as they are separated by a color difference ΔE706. Moreover, it can be not just one direction, but a combination of the lightness direction, chroma direction, and hue angle direction.In addition, although Figure 7 shows an example in which both color 703 and color 704 are corrected, it is also possible to correct only one of the colors to separate them by a color difference ΔE706.

[0065] In S306, the CPU 111 modifies the color conversion table using the result of the degeneracy correction in S305 (performs color degeneracy correction). The original color conversion table is one that converts color 603 to color 703 and color 604 to color 704 in Figure 6. Using the result of S305, the color conversion table is changed to one that converts color 603 to color 707 and color 604 to color 708 in Figure 6 (setting the color conversion method). On the other hand, if it is determined in S303 that no color degeneracy correction is needed, the process in S306 is not performed. In other words, the process in S303 can be rephrased as a process to determine whether or not to modify the color conversion table in S306. As described above, a color conversion table after color degeneracy correction can be generated. The modification of the color conversion table is repeated for the number of color combinations that undergo color degeneracy.

[0066] <Print result> Figure 11 shows an image of the print result of this embodiment. Figure 11(a) shows the print result of color conversion performed on the partial original data of Figure 6 using the color conversion table pre-stored in the storage medium 113 used in S202, and Figure 11(b) shows the print result of color conversion performed in this embodiment. In both Figure 11(a) and Figure 11(b), the gradient region 602 is color converted using the color conversion table that prioritizes color gradation pre-stored in the storage medium 113, so the print results are the same and a smooth gradient is reproduced. On the other hand, when the first solid area 603 and the second solid area 604 are color converted using the color conversion table pre-stored in the storage medium 113, the print result shows reduced discriminability between the solid areas due to color degradation, as shown in Figure 11(a). In this embodiment, by applying the color conversion table corrected in S305 to the solid areas, it is possible to obtain a print result with discriminability close to that of the digital original, which is the partial original data, between the solid areas, as shown in Figure 11(b).

[0067] The color difference between the first solid area 603 and the second solid area 604 in Figure 11(b) is 2.0 or greater, calculated using formula (16) from the results of colorimeter measurements using a colorimeter, according to CIE76. This is a color difference greater than or equal to the minimum value of the range of color differences that a human can distinguish when comparing two colors from a short distance apart, as defined by CIE76. As a result of color reproduction using gamut mapping on a recording medium with a narrow color gamut, it is possible to ensure the minimum level of discrimination that a human can distinguish.

[0068] Furthermore, in the print result of Figure 11(b), the color difference defined by CIE76, calculated from the colorimetric values ​​obtained by measuring the positions of the first solid area 603 and the second solid area 604, is greater than the color difference defined by CIE76, calculated from the colorimetric values ​​obtained by measuring the positions of color 603 at the left end 605 and color 604 at the right end 606 of the gradient area 602.

[0069] According to this embodiment, for image data that does not contain type information, a first region that prioritizes color discrimination and a second region different from the first region are set. The second region is, for example, a gradient region that prioritizes color gradation. By not applying the color conversion method generated from the first region to the second region, a color conversion that can achieve both discrimination and gradation is performed. As a result, a suitable printing result can be obtained in which the gradation of the gradient region is maintained while creating a color difference between solid areas that is visible to humans.

[0070] In this embodiment, a color conversion table that prioritizes color gradation, which is pre-stored in the storage medium 113, is applied to the second region. However, if the color conversion table pre-stored in the storage medium 113 used in S202 is applicable, it may be configured to apply that instead.

[0071] In this embodiment, an example of generating a color conversion table after color degradation correction to be applied to the first region is shown. However, a configuration that applies the color conversion table that prioritizes color discrimination, as described above and stored in the storage medium 113 in advance, is also possible. As a result, it becomes possible to reduce the processing time for generating the color conversion table.

[0072] Furthermore, in this embodiment, a color conversion table pre-stored in the storage medium 113 is used to set the color conversion table, and a color conversion table is created in the same format as that color conversion table. However, for example, in the color conversion in S202, the color conversion may be performed according to a predetermined rule to convert the color relative to the color reproduction range of the printing device 108 from the color reproduction range of the acquired image data, without using the color conversion table stored in the storage medium 113. As a result, it is not necessary to store the color conversion table in the storage medium 113 in advance, and the storage capacity can be reduced. Also, in setting the color conversion method in S204, the color conversion table may not be set, and the color information before and after color conversion may be set in a 1:1 correspondence (so-called dictionary format), or it may be set using a calculation formula if it can be approximated by a calculation formula. As a result, the storage capacity required to store the color conversion method can be reduced compared to using a color conversion table.

[0073] The following explains, using Figures 21(a) to 21(c), cases in which similar effects can be obtained even if the color conversion table used for the first region and the color conversion table used for the second region in S204 are the same. Figure 21(a) shows the relationship between the color space 2001 of the standard display, the color space 2002 of the recording device 108, and colors 2101, 2102, and 2103. Color 2101 is a color that exists in color space 2002, color 2102 is a color that exists on the surface of color space 2002, and color 2103 is a color that exists in color space 2001. Next, Figure 21(b) shows the results of color conversion of colors 2101, 2102, and 2103 using the color conversion table used in S204. In this example, an example using a color conversion method that emphasizes gradation, as shown in Figure 20(b), is shown. However, it is not limited to this, and any color conversion table with different characteristics may be used as long as no problems occur when applied to the second region. Due to gamut mapping, color 2101 is converted to color 2104, color 2102 to color 2105, and color 2103 to color 2106, resulting in color degeneracy. Figure 21(c) shows the results of color degeneracy correction applied to colors 2104, 2105, and 2106. As a result of color degeneracy correction, color 2101 is ultimately converted to color 2107, color 2102 to color 2108, and color 2103 to color 2109. If colors 2101, 2102, and 2103 exist in both the first and second regions, in the first region, these colors will be converted to colors 2107, 2108, and 2109. On the other hand, in the second domain, those colors are converted to colors 2104, 2105, and 2106. In this way, even if the color conversion table used for the first domain and the color conversion table used for the second domain are the same, it is possible to maintain the gradation of colors in the second domain, which prioritizes gradation, while reducing color degeneracy (improving discriminability) in the first domain, which prioritizes discriminability, by performing color degeneracy correction.

[0074] Furthermore, in S204, we will explain a case in which the effect of reducing color degeneracy can be obtained by using different color conversion tables (switching) in the first and second regions, without performing the color degeneracy correction shown in Figure 10. Such a case is, for example, when it is determined in S303 that no color degeneracy has occurred and the process proceeds to S304. An example in which the color conversion method prioritizing discrimination shown in Figure 20(c) is used for the first region and the color conversion method prioritizing gradation shown in Figure 20(b) is used for the second region will be explained using Figure 22(a). Figure 22(a) shows the result of color conversion of colors 2101 and 2102 in Figure 21(a), i.e., colors 2101 and 2102 in the first region, using the color conversion method prioritizing discrimination shown in Figure 20(c). Due to gamut mapping, color 2101 is converted to color 2201, and color 2102 is converted to color 2202. Colors 2101 and 2102 exhibit color degeneration in colors 2104 and 2105, which are converted using the color conversion method prioritizing gradation shown in Figure 20(b). However, no color degeneration occurs in colors 2201 and 2202. In other words, switching the color conversion table between the first and second regions reduces color degeneration. However, there are cases where color degeneration occurs depending on the input color. For example, this occurs when color degeneration is detected in S303 and the process proceeds to S305. Figure 22(b) shows an example where color 2203, which is converted using the color conversion method prioritizing discrimination shown in Figure 20(c), is added to Figure 22(a). Colors 2202 and 2203 are converted to almost the same color, indicating color degeneration. In this case, as explained in the above embodiment, color degeneration can be reduced by performing color degeneration correction. Figure 22(c) shows an example of applying color degradation correction to color 2203. Color 2203 is color-degraded to color 2204, resulting in a reduction of color degradation.

[0075] [Second Embodiment] The second embodiment will now be described in terms of its differences from the first embodiment. In the first embodiment, for image data that does not contain type information, a first region that emphasizes color discrimination and a second region that emphasizes color gradation are set. A configuration was described in which a color conversion that can achieve both discrimination and gradation is performed by not applying the color conversion method generated from the first region to the second region that emphasizes color gradation. However, if the color conversion method is set using all the colors in the first region that emphasizes color discrimination, it may not be possible to generate a color conversion table that guarantees sufficient discrimination.

[0076] Figure 12 is a flowchart illustrating the color conversion process S103 in Figure 3 in the second embodiment. The process in Figure 12 is realized, for example, by the CPU 111 executing a program read from RAM 112. Since S201 to S203 are the same as in the first embodiment, their explanation is omitted. Also, S202 and S1201 and S203 are executed in parallel. Furthermore, the processing may be performed sequentially in the order of S201, S203, and S202.

[0077] In S1201, the CPU 111 sets a third area on the image represented by the image data acquired in S201 to be used to set the color conversion method for the image data, and a fourth area not used to set the color conversion method for the image data (area setting). Setting the color conversion method in this embodiment means generating a color conversion table for gamut mapping. Setting the color conversion method may involve generating a conversion formula or generating a color conversion table; any method that allows a method for performing color conversion is acceptable.

[0078] Figure 13 shows an example of image data acquired in S201 in this embodiment. Figure 13 is an image obtained by simply downsampling the image data of the first solid area 603 and the second solid area 604 in Figure 6 to a lower resolution, and then converting the resolution back to the original resolution using bilinear transformation. In other words, it shows an example of data in which only the solid areas have been edited. Image data generated by image editing applications etc. on PC101 may use data in which some of the image data has undergone resolution transformation or compression. As shown in Figure 13, a single-pixel color area 1301 surrounding the first solid area 603 is generated. Similarly, a single-pixel color area 1302 surrounding the second solid area 604 is generated. The color of color area 1301 is also called color 1301, and the color of color area 1302 is also called color 1302. In Figure 6, there were only two colors, color 603 and color 604, as the solid color area. However, in Figure 13, in addition to colors 603 and 604, colors 1301 and 1302 are generated by the resolution conversion described above. Generally, when the resolution conversion is performed as described above, color 1301, which is generated unintentionally by the user, will be close to color 603, and similarly, color 1302, which is generated unintentionally by the user, will be close to color 604. However, even though they are close colors, the color difference ΔE between color 1301 and color 603, and between color 1302 and color 604, is 2.0 or more, unlike the gradient area. In this embodiment, a single-pixel color area surrounding the solid color area is shown, but if it is not determined to be a gradient area as exemplified in the first embodiment, it may be a color area of ​​one or more pixels surrounding the solid color area.

[0079] Figures 14(a) and 14(b) illustrate color degeneration and its improvement (elimination) in this embodiment. In Figures 14(a) and 14(b), color 1401 is the color obtained by color conversion of color 1301 using gamut mapping. Color 1402 is the color obtained by color conversion of color 1302 using gamut mapping. If a correction is made to increase the inter-color distance in order to correct the color degeneration as described above, a color conversion table will be generated in which color 603 is gamut-mapped to color 1403, color 604 to color 1404, color 1301 to color 1405, and color 1302 to color 1406. As a result, although an inter-color distance is created, it may not be possible to increase the inter-color distance in the device color gamut to a level equivalent to 2.0 or more, or to a level equivalent to the color difference ΔE1406 between color 1403 and color 1404. As a result, while the color 603 of the first solid area 603 and the color 604 of the second solid area 604 are distinguishable on the monitor, they may become indistinguishable in the print output from the printing device 108.

[0080] Therefore, in this embodiment, instead of setting the color conversion method using the color information of all pixels in the first region of the first embodiment, a third region used to set the color conversion method for input image data and a fourth region not used to set the color conversion method for input image data are set, and the color conversion method is set using the color information of the third region. As will be described later, in this embodiment, the third region is set from the input image data, and a color conversion table is generated limited to the color information of the third region. As a result, even when the image data in Figure 14(a) is input, it becomes possible to set a color conversion method suitable for color discrimination in Figure 7, rather than Figure 14(b), and the problem of color differences not being distinguishable in the output of the printing device 108 can be improved.

[0081] In this embodiment, the color information of image data that is identifiable by humans and discriminable in the output of the printing device 108 is defined as a region having a predetermined or larger area in a planar manner, and this region is set as the third region. Therefore, the region in the image data where two or more pixels with the same color information are consecutive vertically and two or more pixels are consecutive horizontally is set as the third region. The setting of the third region in this embodiment will be explained using Figure 8. As shown by the arrow in Figure 8(a), in this embodiment, line processing is performed sequentially on the image data at the pixel level. In the pixel-level processing, it is determined whether the color information of the three surrounding pixels (pixels 801, 802, and 803) of the target pixel (pixel of interest) 800 shown in Figure 8(b) is the same as the color information of the pixel of interest. If the determination result is the same, the four pixels including the pixel of interest are set as the third region. Pixels that have already been set as the third region may be reset as the third region in the pixel-level processing. In this embodiment, the third region is set using the method described above. However, the process is not limited to the above as long as a region with the same color information and a predetermined or larger area in a planar manner can be set. Furthermore, although this embodiment sets up regions with the same color information, in image data compressed using lossy compression such as JPEG, the color information may vary within a predetermined range, even if the original image data has the same color information. Therefore, a range that allows for variation may be set for regions with the same color information, for example, by setting the color difference ΔE to within 1.0 or the difference in RGB values ​​to within a predetermined value.

[0082] As a result of the settings, in this embodiment, for both the image data in Figure 6 and Figure 13, the area filled in black in Figure 15 is set as the third area, and the area filled in white in Figure 15(a) is set as the fourth area. In other words, even if colors 1301 and 1302 that the user did not intend occur, these colors are not taken into consideration when setting the color conversion method for the input image data.

[0083] As shown in Figure 15, in this embodiment, the color 603 of the first solid area 603 and the color 604 of the second solid area 604, which have a planar area of ​​a predetermined or greater size, are set as color information of image data that is identifiable by humans and discriminable in the output of the printing device 108. As shown in Figure 15(b), colors 1301 and 1302 are colors in the fourth area adjacent to the third area, not the third area used to generate the color conversion table after color degeneracy correction (used to set the color conversion method). As described above, since color 1301 is close to color 603 and color 1302 is close to color 604, colors 1301 and 1302 are also color-converted using the color conversion table after color degeneracy correction. In other words, the area to which the color conversion table after color degeneracy correction is applied is the third area and an area including at least a part of the fourth area. In this way, by differentiating the area used to generate the color conversion table after color degradation correction from the area to which the generated color conversion table after color degradation correction is applied, it is possible to prevent unnecessary color degradation correction and obtain an optimal output image.

[0084] Furthermore, Figure 16(b) shows a first region to which the color conversion table that prioritizes color discrimination set in S203 is applied, and a second region to which the color conversion table that prioritizes color discrimination set in S203 is not applied. In Figure 16(b), the second region is shown as a black-filled region, and the first region is shown as a white-filled region. As shown in Figures 16(a) and 16(b), it is desirable to set the conditions for setting the first and second regions, and the conditions for setting the third and fourth regions, so that the third region used to set the color conversion method that prioritizes color discrimination is included in the first region to which the color conversion method that prioritizes color discrimination can be applied. In other words, it is desirable to set the third region, which is used to set the color conversion method that prioritizes color discrimination, not to be the second region to which the color conversion method that prioritizes color discrimination is not applied.

[0085] Next, in S1202, the CPU 111 generates a color conversion table for the first region set in S203 based on the following information.

[0086] Image data acquired by S201 • Color conversion table used in S202, which is pre-stored in the storage medium 113. • Image data color-converted using a color conversion table pre-stored in the storage medium 113 in S202. • Area information set in S1201 The color conversion method is set using the region information set in S1201, but the setting of the color conversion method itself is the same as in the first embodiment, so the explanation is omitted. For the second region, a color conversion table that prioritizes the gradation of colors, which is stored in the storage medium 113 in advance, is set.

[0087] Next, in S1203, CPU111 performs color conversion based on the following information.

[0088] • Area information set in S203 • Color conversion table for the first region set in S1202 • A color conversion table that prioritizes color gradation, pre-stored in the storage medium 113, for the second area set in S203. For the image data acquired in S201, the first region set in S203 is converted using the color conversion table for the first region set in S1202 to generate the color-converted image data. On the other hand, for the second region set in S203, the color-converted image data is converted using the color conversion table that prioritizes color gradation and is pre-stored in the storage medium 113, set in S1202 to generate the color-converted image data. The generated image data is stored in the RAM 112 or the storage medium 113.

[0089] <Print result> Figure 17 shows an image of the print result of this embodiment. Figure 17(a) shows the print result of color conversion using the color conversion table pre-stored in the storage medium 113 used in S202 on the partial original data of Figure 13, and Figure 17(b) shows the print result of color conversion in this embodiment. In both Figure 17(a) and Figure 17(b), the gradient region 602 is color converted using a color conversion table that prioritizes color gradation pre-stored in the storage medium 113, so the print results are the same and a smooth gradient is reproduced. On the other hand, if the first solid area 603 and the second solid area 604 are color converted using the color conversion table pre-stored in the storage medium 113, as in the first embodiment, the print result will have reduced discriminability between the solid areas due to color degradation, as shown in Figure 17(a). In this embodiment, by applying the color conversion table set in S1202, even if colors 1301 and 1302 that the user did not intend occur around the first solid area 603 and the second solid area 604, it is possible to obtain a print result with discriminability close to that of a digital original between the solid areas, as shown in Figure 17(b). The color difference between the first solid area 603 and the second solid area 604 in Figure 17(b) is 2.0 or more in terms of the CIE76 color difference calculated by formula (16) from the results measured by a colorimeter, similar to the first embodiment.

[0090] Furthermore, in the print result of Figure 17(b), the color difference defined by CIE76, calculated from the colorimetric values ​​obtained by measuring the positions of the first solid area 603 and the second solid area 604, is greater than the color difference defined by CIE76, calculated from the colorimetric values ​​obtained by measuring the positions of color 603 at the left end 605 and color 604 at the right end 606 of the gradient area 602.

[0091] Furthermore, if the image data of Figure 6 is input as the next partial original data after the image data of Figure 13, the print result of the next page will be Figure 11(b). In addition, in the print result obtained by the processing of this embodiment, even if colors 1301 and 1302, which are different from those in Figure 13 and are not intended by the user, occur around the first solid area 603 and the first solid area 604, the print results of the first solid area 603 and the second solid area 604 will be exactly the same color as measured by colorimetric results. In other words, in this embodiment, even if colors 1301 and 1302, which are not intended by the user, occur, discriminability can be ensured between the first solid area 603 and the second solid area 604. In addition, if the color values ​​extracted in the third area are the same across pages, the solid areas will have the same print result across pages.

[0092] According to this embodiment, for image data that does not contain type information, a first region that emphasizes color discrimination and a second region that differs from the first region are set. The second region is, for example, a gradient region that emphasizes color gradation. In addition, a third region used to set the color conversion method for the image data and a fourth region not used to set the color conversion method for the image data are set. By setting each region, unnecessary color degradation correction can be prevented, and an appropriate color conversion method can be set based only on the information of the region necessary for color degradation correction (i.e., the third region). As a result, a color conversion result suitable for the printing device 108 can be obtained for the entire image.

[0093] In this embodiment, the color information of image data that is identifiable to humans and discriminable in the output of the printing device 108 is defined as a third region with a predetermined area in a planar manner, where two or more pixels with the same color information are consecutive vertically and two or more pixels are consecutive horizontally. However, the number of consecutive pixels vertically and horizontally may be set according to the output resolution of the printing device 108 and the visual characteristics of the person viewing the output of the printing device 108. As a result, it becomes possible to set the third region more optimally. Furthermore, the user of the printing device 108 may specify the setting conditions for the third region from the user interface (UI) of the printing device 108 or from the information attached to the original data. As a result, it becomes possible to reflect the user's intentions in the setting conditions for the third region.

[0094] In this embodiment, an example is shown in which a region where image quality deteriorates when the color conversion method generated from the third region is applied to image data is set as the second region, and the color conversion method generated from the third region is not applied to the second region to avoid image quality deterioration. However, the first and second regions may also be separated by setting a first region in which no image quality deterioration occurs even when the color conversion method generated from the third region is applied to image data.

[0095] In each embodiment, the user may be able to input an instruction on whether or not to perform color degradation correction. In that case, a UI screen like those shown in Figures 18 and 19 may be displayed on the UI 103 of the PC 101 or on a display unit (not shown) mounted on the printing device 108 to accept user instructions. In the UI screen shown in Figure 18, the user can select the type of color correction using a toggle button. Furthermore, the user can select ON or OFF whether or not to perform "adaptive gamut mapping," which is the process described in each embodiment, using a toggle button. In addition, in the UI screen shown in Figure 19, the ON or OFF of whether or not to perform "adaptive gamut mapping," which is the process described in each embodiment, can be automatically performed according to the selection made by the media selection toggle button. As shown in Figure 19, if plain paper is selected as the recording medium, "adaptive gamut mapping" is performed because the color reproduction gamut is narrow. If glossy paper or coated paper is selected, "adaptive gamut mapping" is not performed because the color reproduction gamut is wide.

[0096] This configuration allows the system to switch whether or not to perform the adaptive gamut mapping described in each embodiment, according to the user's instructions. As a result, the gamut mapping described in each embodiment can be performed when the user wants to reduce the degree of color degradation.

[0097] The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0098] This embodiment includes an image processing device, a method, and a program. (Item 1) An image processing device, An input means for inputting image data, If the image data input by the input means includes a gradient region having a gradient between a first color value and a second color value, and the region of the image other than the gradient region includes a first solid region having only the first color value and a second solid region having only the second color value, A first color conversion means that performs color conversion on the first solid area and the second solid area using a first color conversion method, and performs color conversion on the gradient area using a second color conversion method, Equipped with, The color conversion by the first color conversion means is a conversion from the color gamut represented by the image data to the color gamut that can be reproduced by the image processing device. As a result of the color conversion performed by the first color conversion means, the color difference between the first solid region and the second solid region is greater than the color difference between the region corresponding to the first color value and the region corresponding to the second color value in the gradient region. An image processing apparatus characterized by the following: (Item 2) The image processing apparatus according to item 1, further comprising a first detection means for detecting the gradient region. (Item 3) The image processing apparatus according to item 2, characterized in that the first color conversion means performs color conversion on areas other than the gradient area detected by the first detection means using the first color conversion method. (Item 4) The system further comprises setting means for setting the first color conversion method, The setting means sets the first color conversion method based on the first color value of the first solid area and the second color value of the second solid area. The image processing apparatus according to item 2 or 3, characterized in that it is an image processing apparatus. (Item 5) A storage means for storing a predetermined color conversion method, A second color conversion means that performs color conversion on areas other than the gradient area using the predetermined color conversion method, Furthermore, The setting means sets the first color conversion method by correcting the predetermined color conversion method to eliminate color degeneration that occurs when, as a result of the color conversion performed by the second color conversion means, the color difference between the color value of the first color value after color conversion and the color value of the second color value after color conversion becomes shorter. The image processing apparatus according to item 4, characterized in that (Item 6) The image processing apparatus according to item 5, characterized in that the setting means sets the predetermined color conversion method as the first color conversion method when no color degradation occurs as a result of the color conversion performed by the second color conversion means. (Item 7) The image processing apparatus according to item 5 or 6, characterized in that the setting means corrects the predetermined color conversion method so that the color difference is at least a predetermined value. (Item 8) The image processing apparatus according to item 7, characterized in that the predetermined value is ΔE = 2.0. (Item 9) The image processing apparatus according to any one of items 5 to 8, characterized in that the setting means corrects the predetermined color conversion method so as to eliminate the color difference in at least one of the directions of brightness, saturation, and hue angle. (Item 10) If the region other than the gradient region includes a third solid region having only the first color value and a fourth solid region having only the second color value, and there is a first color region having the third color value surrounding the third solid region, and a second color region having the fourth color value surrounding the fourth solid region, As a result of the color conversion performed by the first color conversion means, the color value of the first solid area and the color value of the third solid area are equal, and the color value of the second solid area and the color value of the fourth solid area are equal. The image processing apparatus according to item 4, characterized in that (Item 11) The image processing apparatus according to item 10, further comprising a second detection means for detecting the third solid region and the fourth solid region. (Item 12) The image processing apparatus according to item 10 or 11, characterized in that the setting means sets the first color conversion method based on the first color value of the third solid area and the second color value of the fourth solid area, and does not set the first color conversion method based on the third color value of the first color area and the fourth color value of the second color area. (Item 13) The image processing apparatus according to any one of items 1 to 12, characterized in that the first color conversion method and the second color conversion method are different from each other. (Item 14) The image processing apparatus according to item 13, characterized in that the first color conversion method is a color conversion method that does not perform compression within the color gamut reproducible by the image processing apparatus, and the second color conversion method is a color conversion method that performs compression within the color gamut reproducible by the image processing apparatus. (Item 15) The system further includes a receiving means for receiving an instruction on whether or not to perform a color conversion using the first color conversion means, The color conversion by the first color conversion means is performed when the receiving means receives an instruction to perform the color conversion by the first color conversion means. An image processing apparatus according to any one of items 1 to 14, characterized in that (Item 16) The image processing apparatus according to item 15, characterized in that the receiving means receives the selection of a predetermined type of recording medium as an instruction to perform color conversion by the first color conversion means. (Item 17) The image processing apparatus according to item 16, characterized in that the predetermined type of recording medium is plain paper. (Item 18) The image processing apparatus according to any one of items 1 to 17, characterized in that the image processing apparatus is an inkjet recording apparatus. (Item 19) The image processing apparatus according to any one of items 1 to 18, characterized in that the image data is bitmap image data that does not include type information on a pixel-by-pixel basis. (Item 20) A method performed in an image processing device, The input process involves entering image data, If the image data input in the input step includes a gradient region having a gradient between a first color value and a second color value, and the region of the image other than the gradient region includes a first solid region having only the first color value and a second solid region having only the second color value, A first color conversion step in which a color conversion is performed on the first solid area and the second solid area using a first color conversion method, and a color conversion is performed on the gradient area using a second color conversion method, It has, The color conversion in the first color conversion step is a conversion from the color gamut represented by the image data to the color gamut that can be reproduced by the image processing device. As a result of the color conversion performed in the first color conversion step, the color difference between the first solid region and the second solid region is greater than the color difference between the region corresponding to the first color value and the region corresponding to the second color value in the gradient region. A method characterized by the following: (Item 21) A program for causing a computer to function as one of the means of an image processing apparatus described in any one of items 1 through 19. [Explanation of symbols]

[0099] 101 Image processing device: 108 Recording device: 102, 111 CPU: 104, 112 RAM: 105, 113 Storage medium

Claims

1. An image processing device, An input means for inputting image data, If the image data input by the input means includes a gradient region having a gradient between a first color value and a second color value, and the region of the image other than the gradient region includes a first solid region having only the first color value and a second solid region having only the second color value, A first color conversion means that performs color conversion on the first solid area and the second solid area using a first color conversion method, and performs color conversion on the gradient area using a second color conversion method, Equipped with, The color conversion by the first color conversion means is a conversion from the color gamut represented by the image data to the color gamut that can be reproduced by the image processing device. As a result of the color conversion performed by the first color conversion means, the color difference between the first solid region and the second solid region is greater than the color difference between the region corresponding to the first color value and the region corresponding to the second color value in the gradient region. An image processing apparatus characterized by the following:

2. The image processing apparatus according to claim 1, further comprising a first detection means for detecting the gradient region.

3. The image processing apparatus according to claim 2, characterized in that the first color conversion means performs color conversion on areas other than the gradient area detected by the first detection means using the first color conversion method.

4. The system further comprises setting means for setting the first color conversion method, The setting means sets the first color conversion method based on the first color value of the first solid area and the second color value of the second solid area. The image processing apparatus according to claim 2.

5. A storage means for storing a predetermined color conversion method, A second color conversion means that performs color conversion on areas other than the aforementioned gradient region using the predetermined color conversion method, Furthermore, The setting means sets the first color conversion method by correcting the predetermined color conversion method to eliminate color degeneration that occurs when, as a result of the color conversion performed by the second color conversion means, the color difference between the color value of the first color value after color conversion and the color value of the second color value after color conversion becomes shorter. The image processing apparatus according to feature 4.

6. The image processing apparatus according to claim 5, characterized in that the setting means sets the predetermined color conversion method as the first color conversion method when no color degradation occurs as a result of the color conversion performed by the second color conversion means.

7. The image processing apparatus according to claim 5, characterized in that the setting means corrects the predetermined color conversion method so that the color difference is at least a predetermined value.

8. The image processing apparatus according to claim 7, characterized in that the predetermined value is ΔE = 2.

0.

9. The image processing apparatus according to claim 5, characterized in that the setting means corrects the predetermined color conversion method so as to eliminate the color difference in at least one of the brightness direction, saturation direction, and hue angle direction.

10. If the region other than the gradient region includes a third solid region having only the first color value and a fourth solid region having only the second color value, and there is a first color region having the third color value surrounding the third solid region, and a second color region having the fourth color value surrounding the fourth solid region, As a result of the color conversion performed by the first color conversion means, the color value of the first solid area and the color value of the third solid area are equal, and the color value of the second solid area and the color value of the fourth solid area are equal. The image processing apparatus according to feature 4.

11. The image processing apparatus according to claim 10, further comprising a second detection means for detecting the third solid region and the fourth solid region.

12. The image processing apparatus according to claim 10, characterized in that the setting means sets the first color conversion method based on the first color value of the third solid area and the second color value of the fourth solid area, and does not set the first color conversion method based on the third color value of the first color area and the fourth color value of the second color area.

13. The image processing apparatus according to claim 1, characterized in that the first color conversion method and the second color conversion method are different from each other.

14. The image processing apparatus according to claim 13, characterized in that the first color conversion method is a color conversion method that does not perform compression within a color gamut reproducible by the image processing apparatus, and the second color conversion method is a color conversion method that performs compression within a color gamut reproducible by the image processing apparatus.

15. The system further includes a receiving means for receiving an instruction on whether or not to perform color conversion by the first color conversion means, The color conversion by the first color conversion means is performed when the receiving means receives an instruction to perform the color conversion by the first color conversion means. The image processing apparatus according to feature 1.

16. The image processing apparatus according to claim 15, characterized in that the receiving means receives the selection of a predetermined type of recording medium as an instruction to perform color conversion by the first color conversion means.

17. The image processing apparatus according to claim 16, characterized in that the predetermined type of recording medium is plain paper.

18. The image processing apparatus according to claim 1, characterized in that the image processing apparatus is an inkjet recording apparatus.

19. The image processing apparatus according to claim 1, characterized in that the image data is bitmap image data that does not include type information on a pixel-by-pixel basis.

20. A method performed in an image processing device, The input process involves entering image data, If the image data input in the input step includes a gradient region having a gradient between a first color value and a second color value, and the region of the image other than the gradient region includes a first solid region having only the first color value and a second solid region having only the second color value, A first color conversion step in which a color conversion is performed on the first solid area and the second solid area using a first color conversion method, and a color conversion is performed on the gradient area using a second color conversion method, It has, The color conversion in the first color conversion step is a conversion from the color gamut represented by the image data to the color gamut that can be reproduced by the image processing device. As a result of the color conversion performed in the first color conversion step, the color difference between the first solid region and the second solid region is greater than the color difference between the region corresponding to the first color value and the region corresponding to the second color value in the gradient region. A method characterized by the following:

21. A program for causing a computer to function as each means of the image processing apparatus according to any one of claims 1 to 19.

Images